Circuit boards are becoming more and more densely packed with electronic devices as the need for power, memory and additional capabilities increases. As a result the heat generated by these electronic devices also increases. The heat that is generated by an electronic device must be transferred away from the electronic device or the performance of the electronic device(s) will deteriorate. The problem of dissipating heat from electronic devices mounted on circuit boards gets worse when the piece of equipment employing the circuit board is mounted within a housing. For example, fiber optic transmitter/receiver modules that include circuit boards are often environmentally sealed in a housing to prevent damage from the elements. As a result, the ability to dissipate heat from the electronic devices mounted on the circuit boards becomes challenging. The environmental housing's only mode of heat transfer to the ambient is natural convection. The transmitter/receiver module's only mode of heat transfer to the environmental housing is conduction.
A classic thermal management technique uses thermal vias to dissipate heat. The thermal vias are located in a copper pad of a printed circuit board, under the device that needs cooling. A heat sink pad of a device is soldered to the copper pad of the circuit board. During operation of the device, heat is transferred from the device's heat sink pad to the copper pad on the primary side of the circuit board. The heat is then transferred through the thermal vias to the far (secondary) side of the circuit board and to the housing of the transmitter/receiver module. The heat is then transferred by conduction from the transmitter/receiver module to the unit's environmental housing. As the component density in an electronic module increases, it becomes difficult to use classical thermal vias to dissipate heat.